Method and system for providing compressed substantially oxygen-free exhaust gas for industrial purposes

ABSTRACT

A method and system of providing compressed substantially oxygen-free exhaust gas for industrial purposes including the steps of extracting exhaust gas from a lean burn engine consuming a mixture of natural gas fuel and air, passing the extracted exhaust gas through a cooling step to cause entrained water vapor therein to condense out, separating and disposing of the condensed water, measuring the oxygen content of the exhaust gas, using the measurement to regulate the quantity of natural gas fed into an igniter into which the exhaust gas is also fed so that substantially all of the oxygen in the exhaust gas is consumed by combustion with the natural gas in the igniter to provide at an outlet of the igniter substantially oxygen-free exhaust gas, and compressing the substantially oxygen-free exhaust gas to provide compressed exhaust gas for industrial applications.

REFERENCE TO PENDING APPLICATIONS

This is application is not related for purposes of priority to anyexisting United States or foreign patent application.

REFERENCE TO MICROFICHE APPENDIX

This application is not referenced to any microfiche appendix.

FIELD OF THE INVENTION

The present invention is generally directed toward a method of providingcompressed substantially oxygen-free exhaust gas for industrialpurposes. More specifically, the present invention is directed toward asystem for providing substantially dry oxygen-free exhaust gas thatemploys a combustor to burn natural gas with the exhaust gas from a leanburn engine to produce substantially oxygen-free exhaust gas.

BACKGROUND OF THE INVENTION

Most oil producing subterranean formations are characterized bypressurized gas. In some parts of the work hydrocarbon bearingformations have pressures sufficient to force liquid hydrocarbons (crudeoil) to the earth's surface. In other parts of the world, the gaspressure is not sufficient to force liquid hydrocarbons to the earth'ssurface. However, in such formations, the presence of gas isnevertheless important since in many formations a gas drive is requiredto move liquid hydrocarbons from within the formation to the site of aproducing well or wells.

As crude oil is extracted from a subterranean reservoir, the reservoirgas pressure decreases. As the gas pressure decreases, crude oilproduction rates usually fall. For these and other reasons, it has beenfound desirable in producing many subterranean formations to maintaingas pressure within the formations.

The characteristics of gas injected into a well can be critical. Freeoxygen contained in injected gas can cause plugging of formations.Further free oxygen can result in bacteria growth that can plug aproducing formation, and corrode tubulars in the producing well.

Ideally, gas injected into a reservoir to augment the production ofliquid hydrocarbons should be oxygen-free. Therefore, when treating gasprior to injection, a most important step is to remove substantially allfree oxygen.

The present invention provides a process for generating substantiallyoxygen-free exhaust gas that is particularly useful for injection intohydrocarbon bearing formations.

Examples of the use of exhaust gas from an engine for industrialpurposes and examples of the use of exhaust gas to augment liquidhydrocarbon production are found in the following United States patents:

U.S. PAT. NO. INVENTOR(S) TITLE 1,868,755 Mount Dehydrator 1,945,407Adair et al. Process of Purifying Gases 2,240,550 Conlon, Jr. Method ofRetuning Gas to Gas-Producing Formations 2,825,408 Watson Oil RecoveryBy Subsurface Thermal Processing 3,004,601 Bodine Method and Apparatusfor Augmenting Oil Recovery from Wells by Refrigeration 3,100,528Plummer, et al. Method for Using Inert Gas 3,137,344 Wiemer MinimizingLoss of Driving Fluids in Secondary Recovery 3,381,523 Nettles Methodand Apparatus for Supplying Gas Under Pressure 3,653,438 Wagner Methodof Recovery of Petroleum Deposits 3,908,762 Redford Method forEstablishing Communication Path in viscous Petroleum-ContainingFormations Including Tar Sand Deposits for Use in Oil RecoveryOperations 4,324,291 Wong et al. Viscous Oil Recovery Method 4,325,432Henry Method of Oil Recovery 4,533,374 Haag Method for Reducing AirPollution 4,546,829 Martin et al. Enhanced Oil Recovery Process4,593,763 Burke Carbon Dioxide Well Injection Method 4,891,939 BrighentiSystem for the Cryogenic Processing and Storage of Combustion Productsof Heat Engines 5,232,049 Christiansen, Sequentially flooding aSubterranean et al. Hydrocarbon-Bearing Formation with a Repeating Cycleof Immiscible Displacement Gases 5,988,280 Crawford et al. Use of EngineHeat in Treating a Well Bore 6,039,116 Stevenson et al. Oil and GasProduction with Periodic Gas Injection

BRIEF SUMMARY OF THE INVENTION

This invention is a method and a system for providing substantiallyoxygen-free exhaust gas useful for industrial purposes and particularlyuseful for injection into subterranean formations to augment theproduction of hydrocarbons. The method includes the steps of: 1)extracting exhaust gas from a lean burn natural gas fuel consumingengine; 2) passing the gas from Step 1 through a catalytic converter; 3)cooling the gas from Step 2 to provide a cooled exhaust gas; 4) passingthe cooled exhaust gas from Step 3 through a scrubber/separator by whichentrained water is extracted to provide dry exhaust gas; 5) conductingthe dry exhaust gas into an igniter vessel; (6) flowing natural gas intothe igniter vessel in proportion to the level of oxygen in the exhaustgas; (7) combusting the natural gas and oxygen in the exhaust gas; and(8) compressing the substantially oxygen-free exhaust gas for industrialpurposes such as for injecting into a hydrocarbon producing formation.

A system for practicing the method of this invention includes a leanburn natural gas fuel consuming engine that produces exhaust gas. Acatalytic converter is connected to receive the exhaust gas from theengine. An air cooler is employed by which water vapor is extracted tothereby provide substantially water-free exhaust gas. The oxygen contentof the substantially water-free exhaust gas is measured by use of anoxygen analyzer. This measurement is used to regulate the ratio ofexhaust gas and natural gas in an igniter where the oxygen is consumedby combustion with the natural gas. The exhaust gas, having minimaloxygen, is then passed through compression and cooling steps to causeany remaining entrained water vapor to condense out. The extracted watervapor is separated and disposed of to provide substantially dry andsubstantially oxygen-free exhaust gas, which is then compressed so thatit can be used industrially, such as for injecting into a producing oilor gas-bearing formation.

A better understanding of the invention will be obtained from thefollowing description and claims taken in conjunction with the attacheddrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing is a block diagram that may also be described as a flowdiagram that illustrates a method and a system employing a lean burnnatural gas combustion engine having a drive shaft connected to amulti-stage compressor. Exhaust gas from the engine is passed through acatalytic converter, cooled and then subjected to compression. Condensedwater is extracted to provide a substantially water-free exhaust gas.The exhaust gas is then measured to detect the oxygen content thereof.The exhaust gas is then fed into an igniter that also receives acontrolled quantity of natural gas. Combustion within the igniterconsumes any and substantially all the oxygen remaining in the exhaustgas to provide substantially oxygen-free exhaust gas for industrialpurposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, and first to FIG. 1, a system that can beused for practicing a method of this invention is shown. The systemmakes use of the exhaust gas output of a lean burn internal combustionnatural gas engine, the engine being indicated by the numeral 10. Suchan engine can be the kind utilized in an automobile, a truck or anindustrial engine. The size of the engine will be determined by thequantity of gas required. If more gas is required than can be producedby a single engine, then multiple separate engines may be utilized. Theengine 10 utilizes natural gas fuel mixed with ambient air that iscombusted within the engine to produce energy output in the form of arotating drive shaft 12. As a consequence of the combustion of the fueland air within engine 10, exhaust gas is produced at an exhaust 14.

Gas from exhaust 14 is passed through a catalytic converter 16. In thecatalytic converter, heated catalysts react with deleterious componentsof the exhaust gas to substantially neutralize such components toprovide an output from the catalytic converter that is moreenvironmentally acceptable.

The exhaust gas having passed through catalytic converter 16 is reducedto a lower temperature in an air cooler 18. From air cooler 18, theexhaust gas is fed into a scrubber/separator 20 in which any entrainedwater is separated with the water passing out through a discharge line22 and the exhaust gas passing through a conduit 24. Exhaust gasproduced by lean burn engines characteristically has excess oxygen thatis not sufficiently removed merely by a sequence of compressing andcooling steps. The essence of this invention is a provision of a methodand system whereby exhaust gas from a lean burn engine can be treated insuch a way that it is useful for industrial applications including, as aspecific but not limiting example, introduction into subterranean oil orgas producing formations to augment production.

For this purpose, exhaust gas appearing in conduit 24 is fed into a gasigniter/combustion chamber which, for brevity, will hereinafter bereferred to as a combustion chamber 26. Combustion chamber 26 is asystem that mixes any significant oxygen contained within the exhaustgas stream in conduit 24 with a gas fuel so that, by combustion, theoxygen is depleted. For this purpose an igniter that constantly providesa spark or other means for initiating combustion is provided within thecombustion chamber 26.

The method of this invention includes the steps of supplying a gaseousfuel into combustion chamber 26 to combine with oxygen contained withinthe exhaust gas appearing in conduit 24. For this reason, a source ofnatural gas 28 is utilized. When the system of this invention isemployed in an oil field to augment the secondary recovery of petroleum,a source of natural gas is frequently inherently available. In otherinstances, the source of natural gas may be from a supply line used tosupply gas for residential or industrial heating purposes.

The quantity of flow from the source of natural gas 28 is regulated by acontrol valve 30, the output at 32 which represents a controlled gassource.

Gas from control gas source 32 flows into exhaust conduit 24 tointimately mix with the exhaust gas passing out of scrubber/separator 20and passing into combustion chamber 26. Thus, the inflow into combustionchamber 26 is exhaust gas having natural gas admixed therewith, thepurpose of the natural gas is to combine, by combustion, with oxygenfound within the exhaust gas stream appearing at exhaust gas conduit 24to thereby burn and neutralize the oxygen content.

The output of combustion chamber 26 includes the exhaust gases fromconduit 24 plus the results of combustion of natural gas flowing intothe combustion chamber from gas source 32. This oxygen-neutralizedexhaust gas flows through conduit 34 to a scrubber/separator 36 of thetype similar to that identified by the numeral 20. Fromscrubber/separator entrained water is carried away by water pipe 38 thatfeeds into a water disposal 40 along with the water from the firstscrubber/separator 20 conveyed by water discharge line 22. The purposeof combustion chamber 26 is to mix oxygen occurring in the exhaust gasstream from lean burn engine 10 with gas and the mixture combusted—thatis, neutralized, to form substantially nitrogen and carbon dioxide. Itis important that the correct quantity of natural gas be supplied fromthe gas source 28—that is, it is important that control valve 30 beaccurately and continuously operated in such a way as to introduce aquantity of natural gas into combustor chamber 26 as is required forcomplete combustion of oxygen contained in the exhaust gas stream. Forthis purpose, an oxygen analyzer 42 is connected to sample gas flowingthrough conduit 34. Oxygen analyzer 42 provides an electrical signal byway of conductor 44 connected to a controller 46 that in turn provides asignal at 48 to regulate control valve 30. More specifically, controller46 responds to the electrical signal appearing at conductor 44 toprovide a control signal at 48 that may be electrical or hydraulic,depending upon the type of control valve 30. When oxygen analyzer 42detects the presence of oxygen in the exhaust gas flowing throughconduit 24, a signal is sent to controller. 46 to open control valve 30to a greater degree, to allow more natural gas to be introduced intocombustion chamber 26 to thereby combine with and neutralize the oxygen.On the other hand, if oxygen analyzer 42 detects a reduced amount ofoxygen in the exhaust gas appearing in conduit 34, then a reducedquantity of natural gas is supplied to the combustion chamber. In otherwords, the closed circuit function of oxygen analyzer 42, controller 46,control valve 30 and combustion chamber 26 is to continuously regulatethe amount of natural gas supplied to the combustion chamber tosubstantially neutralize oxygen occurring within the exhaust gas streamat conduit 24 to thereby provide gas that flows through conduit 34 toscrubber/separator 36 that is substantially oxygen-free.

Oxygen neutralized exhaust gas appearing at the outlet conduit 50 fromscrubber/separator 36 is fed into the input of a multi-stage compressor51. In the arrangement as illustrated, compressor 51 has four stages ofcompression with intermediate coolers 52, 54 and 56. Cooler 52 isbetween first compressor stage 1 and second compressor stage 2; cooler54 is between compressor stage 2 and compressor stage 3; and cooler 56is between compressor stages 3 and 4. The compressed gas at the output58 of the 4^(th) compression stage is substantially oxygen-free and atan elevated pressure suitable to be used for industrial purposes. Aspreviously stated, an example of an ideal use of the substantiallyoxygen-free exhaust gas at output 58 is injection into a subterraneanhydrocarbon producing formation to maintain the pressure of theformation to thereby augment the production of liquefied petroleum.

The use of a multi-stage compressor 51 with its companion coolers 52, 54and 56 is by example only. However, for most efficient generation ofengine exhaust gas, it is preferable that engine 10 have a load—that is,that it does work. This is achieved by using the available energy fromengine 10 to drive compressor 51 to produce the ultimate pressurerequired at output 58.

The substantially oxygen-free exhaust gas appearing at 58 and asproduced by the system and method of this invention as illustrated inthe drawing is substantially composed of nitrogen and carbon dioxide.The system confines the carbon dioxide and nitrogen as produced by theengine for industrial use such as injection into a subterraneanformation and thereby makes use of the carbon dioxide and nitrogen thatwould otherwise pass to the atmosphere.

The claims and the specification describe the invention presented andthe terms that are employed in the claims draw their meaning from theuse of such terms in the specification. The same terms employed in theprior art may be broader in meaning than specifically employed herein.Whenever there is a question between the broader definition of suchterms used in the prior art and the more specific use of the termsherein, the more specific meaning is meant.

While the invention has been described with a certain degree ofparticularity, it is manifest that many changes may be made in thedetails of construction and the arrangement of components withoutdeparting from the spirit and scope of this disclosure. It is understoodthat the invention is not limited to the embodiments set forth hereinfor purposes of exemplification, but is to be limited only by the scopeof the attached claims, including the full range of equivalency to whicheach element thereof is entitled.

1. A method of providing compressed substantially oxygen-free exhaustgas for industrial purposes comprising: (1) extracting exhaust gas froma lean burn engine consuming natural gas fuel and air, the extractedexhaust gas having oxygen therein; (2) passing said extracted exhaustgas through a cooling step in which the exhaust gas is cooled to causeat least a substantial portion of entrained water vapor therein tocondense out leaving substantially water-free exhaust gas; (3)introducing said substantially water-free exhaust gas and natural gasinto a combustion chamber having means of igniting combustion thereinwhereby these gases are combusted to produce oxygen-neutralized exhaustgas; (4) measuring for oxygen in said oxygen neutralized exhaust gas;(5) using the measurement obtained in Step (4) to regulate the ratio ofnatural gas to substantially water-free exhaust gas into said combustionchamber to ensure that substantially all oxygen in said substantiallywater-free exhaust gas is depleted as a consequence of combustion inStep (3) providing a substantially oxygen-free exhaust gas; and (6)compressing said substantially oxygen-free exhaust gas to providecompressed gas for industrial applications.
 2. A method of providingcompressed substantially oxygen-free exhaust gas according to claim 1,including, after Step (1) of passing said exhaust gas through acatalytic converter before Step (2).